/metrics endpoint is way too slow under Wildfly 8

This was earlier reported on #175, which was closed by adding a footnote in the documentation.

I’m running Wildfly instances in a few Docker containers and the /metrics entpoint takes way too long. From inside the container:

$ time curl http://localhost:28686/metrics

## clipped output (metrics are returned as filtered)

real	1m28.087s
user	0m0.020s
sys	0m0.024s

We are having better results using Glassfish 3.1.2.2 or Wildfly 10. Any particular reason why this is taking so long under Wildfly 8? Any tips on how to filter metrics to make the endpoint faster?

Otherwise, we’ll have to configure Prometheus with a scrape_interval of at least 2 minutes!

[n3v3rf411]

I’m having the same same issue as yours where the usual scrape time takes about 43 seconds even with the latest code. In my case, I already the know the object names in advance so I set whitelistObjectNames accordingly like as follows:

---
whitelistObjectNames: ["jboss.as:subsystem=undertow,server=*,http-listener=*"]
lowercaseOutputName: true
lowercaseOutputLabelNames: true
rules:
  - pattern: "^jboss.as<subsystem=undertow, server=(.+), http-listener=(.+)><>(bytes_.+|error_count|processing_time|request_count):"
    attrNameSnakeCase: true
    name: wildfly_undertow_$3
    labels:
      server: $1
      http_listener: $2

This improves scrape time from 43s to only 0.028s.

[finkr]

I have submitted a PR to add whitelistObjectNames, see #284

Thanks @n3v3rf411